Methods of making bis-tridentate carbene complexes of ruthenium and osmium

ABSTRACT

Novel polydentate carbene complexes of ruthenium and formulations containing the same are provided. Organic light emitting device containing the novel polydentate carbene complexes of ruthenium in an emissive layer are also provided. The novel polydentate carbene complexes of ruthenium may be particularly useful in OLEDs to provide devices having improved performance.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. application Ser. No.13/033,160, filed Feb. 23, 2011, the disclosure of which is herebyexpressly incorporated by reference in its entirety.

PARTIES TO A JOINT RESEARCH AGREEMENT

The claimed invention was made by, on behalf of, and/or in connectionwith one or more of the following parties to a joint universitycorporation research agreement: Regents of the University of Michigan,Princeton University, The University of Southern California, and theUniversal Display Corporation. The agreement was in effect on and beforethe date the claimed invention was made, and the claimed invention wasmade as a result of activities undertaken within the scope of theagreement.

FIELD OF THE INVENTION

The present invention relates to methods of making carbene complexes,and more specifically, to methods of making bis-tridentate complexes ofruthenium and osmium.

BACKGROUND

Opto-electronic devices that make use of organic materials are becomingincreasingly desirable for a number of reasons. Many of the materialsused to make such devices are relatively inexpensive, so organicopto-electronic devices have the potential for cost advantages overinorganic devices. In addition, the inherent properties of organicmaterials, such as their flexibility, may make them well suited forparticular applications such as fabrication on a flexible substrate.Examples of organic opto-electronic devices include organic lightemitting devices (OLEDs), organic phototransistors, organic photovoltaiccells, and organic photodetectors. For OLEDs, the organic materials mayhave performance advantages over conventional materials. For example,the wavelength at which an organic emissive layer emits light maygenerally be readily tuned with appropriate dopants.

OLEDs make use of thin organic films that emit light when voltage isapplied across the device. OLEDs are becoming an increasinglyinteresting technology for use in applications such as flat paneldisplays, illumination, and backlighting. Several OLED materials andconfigurations are described in U.S. Pat. Nos. 5,844,363, 6,303,238, and5,707,745, which are incorporated herein by reference in their entirety.

One application for phosphorescent emissive molecules is a full colordisplay. Industry standards for such a display call for pixels adaptedto emit particular colors, referred to as “saturated” colors. Inparticular, these standards call for saturated red, green, and bluepixels. Color may be measured using CIE coordinates, which are wellknown to the art.

One example of a green emissive molecule is tris(2-phenylpyridine)iridium, denoted Ir(ppy)₃, which has the following structure:

In this, and later figures herein, we depict the dative bond fromnitrogen to metal (here, Ir) as a straight line.

As used herein, the term “organic” includes polymeric materials as wellas small molecule organic materials that may be used to fabricateorganic opto-electronic devices. “Small molecule” refers to any organicmaterial that is not a polymer, and “small molecules” may actually bequite large. Small molecules may include repeat units in somecircumstances. For example, using a long chain alkyl group as asubstituent does not remove a molecule from the “small molecule” class.Small molecules may also be incorporated into polymers, for example as apendent group on a polymer backbone or as a part of the backbone. Smallmolecules may also serve as the core moiety of a dendrimer, whichconsists of a series of chemical shells built on the core moiety. Thecore moiety of a dendrimer may be a fluorescent or phosphorescent smallmolecule emitter. A dendrimer may be a “small molecule,” and it isbelieved that all dendrimers currently used in the field of OLEDs aresmall molecules.

As used herein, “top” means furthest away from the substrate, while“bottom” means closest to the substrate. Where a first layer isdescribed as “disposed over” a second layer, the first layer is disposedfurther away from substrate. There may be other layers between the firstand second layer, unless it is specified that the first layer is “incontact with” the second layer. For example, a cathode may be describedas “disposed over” an anode, even though there are various organiclayers in between.

As used herein, “solution processible” means capable of being dissolved,dispersed, or transported in and/or deposited from a liquid medium,either in solution or suspension form.

A ligand may be referred to as “photoactive” when it is believed thatthe ligand directly contributes to the photoactive properties of anemissive material. A ligand may be referred to as “ancillary” when it isbelieved that the ligand does not contribute to the photoactiveproperties of an emissive material, although an ancillary ligand mayalter the properties of a photoactive ligand.

As used herein, and as would be generally understood by one skilled inthe art, a first “Highest Occupied Molecular Orbital” (HOMO) or “LowestUnoccupied Molecular Orbital” (LUMO) energy level is “greater than” or“higher than” a second HOMO or LUMO energy level if the first energylevel is closer to the vacuum energy level. Since ionization potentials(IP) are measured as a negative energy relative to a vacuum level, ahigher HOMO energy level corresponds to an IP having a smaller absolutevalue (an IP that is less negative). Similarly, a higher LUMO energylevel corresponds to an electron affinity (EA) having a smaller absolutevalue (an EA that is less negative). On a conventional energy leveldiagram, with the vacuum level at the top, the LUMO energy level of amaterial is higher than the HOMO energy level of the same material. A“higher” HOMO or LUMO energy level appears closer to the top of such adiagram than a “lower” HOMO or LUMO energy level.

As used herein, and as would be generally understood by one skilled inthe art, a first work function is “greater than” or “higher than” asecond work function if the first work function has a higher absolutevalue. Because work functions are generally measured as negative numbersrelative to vacuum level, this means that a “higher” work function ismore negative. On a conventional energy level diagram, with the vacuumlevel at the top, a “higher” work function is illustrated as furtheraway from the vacuum level in the downward direction. Thus, thedefinitions of HOMO and LUMO energy levels follow a different conventionthan work functions.

More details on OLEDs, and the definitions described above, can be foundin U.S. Pat. No. 7,279,704, which is incorporated herein by reference inits entirety.

SUMMARY OF THE INVENTION

A method of making a metal complex having the formula I is provided.Q₁-M-Q₂  Formula IThe method comprises mixing a salt of formula MX₂L_(n) with precursorsof carbenes Q₁ and Q₂, wherein Q₁ and Q₂ are independently selected froma compound of formula II,

a carbene forming agent, solvent, and heating the reaction mixture. Q₁and Q₂ can be the same or different.

In the metal salt MX₂L_(n), M is a second or third row transition metalin the +2 oxidation state, X is a halogen, L is a ligand coordinated toM selected from the group consisting of DMSO, THF, and CH₃CN, and n is 2to 4.

Rings A and B are independently selected from the group consisting of:(a) a 5-membered heterocyclic group, (b) an 8- to 12-membered bicyclicgroup having from 0 to 6 ring heteroatoms, (c) an 11- to 18-memberedtricyclic group having from 0 to 7 ring heteroatoms, (d) an 11- to14-membered fused tricyclic group having from 0 to 6 ring heteroatoms,and (e) an 14- to 18-membered fused tetracyclic group having from 0 to 7ring heteroatoms. Ring A and/or ring B may form a salt, a is 0 to 4, andb is 0 to 4.

X¹ is selected from C—R¹ and N, X² is selected from C—R² and N, and X³is selected from C—R³ and N.

In one aspect, R¹ and R², or R² and R³ are linked to form a 5- or6-membered cyclic group, an 8- to 10-membered fused bicyclic group, an11- to 14-membered fused tricyclic group, which may be optionallysubstituted with one or more substituents independently selected fromhydrogen, deuterium, halide, alkyl, cycloalkyl, heteroalkyl, arylalkyl,alkoxy, aryloxy, amino, silyl, alkenyl, cycloalkenyl, heteroalkenyl,alkynyl, aryl, heteroaryl, acyl, carbonyl, carboxylic acids, ester,nitrile, isonitrile, sulfanyl, sulfinyl, sulfonyl, phosphino, andcombinations thereof;

In one aspect, R¹ and an R^(A) are linked to form a 5- or 6-memberedcyclic group, or an 8- to 10-membered fused bicyclic group.

In one aspect, R³ and an R^(B) are linked to form a 5- or 6-memberedcyclic group, or an 8- to 10-membered fused bicyclic group.

The groups R^(A), R^(B), R¹, R², R³, and R′ are independently selectedfrom the group consisting of hydrogen, deuterium, halide, alkyl,cycloalkyl, heteroalkyl, arylalkyl, alkoxy, aryloxy, amino, silyl,alkenyl, cycloalkenyl, heteroalkenyl, alkynyl, aryl, heteroaryl, acyl,carbonyl, carboxylic acids, ester, nitrile, isonitrile, sulfanyl,sulfinyl, sulfonyl, phosphino, and combinations thereof.

In one aspect, M is ruthenium or osmium.

In one aspect, the carbene forming agent is selected from silver(I)oxide and copper(I) alkoxide. In one aspect, the copper(I) alkoxide iscopper(I) tert-butoxide.

In one aspect, the metal salt has the formula RuX₂(DMSO)₄. In oneaspect, the metal salt has the formula RuCl₂(DMSO)₄.

In one aspect, the metal salt has the formula OsX₂(DMSO)₄. In oneaspect, the metal salt has the formula RuCl₂(DMSO)₄.

In one aspect, the solvent comprises a polar solvent. In one aspect, thepolar solvent comprises an alcohol. In one aspect, the alcohol isselected from the group consisting of 2-methoxyethanol, 2-ethoxyethanol,and mixtures thereof.

In one aspect, the precursors of carbenes Q₁ and Q₂ are independentlyselected from a compound of formula III:

In the compound of formula III, the dashed line represents an optionalbond, X⁴ is selected from N—R′, O, and S, X⁵ is selected from N—R′, O,and S, and A is a counterion.

Specific, non-limiting examples of carbene precursors are provided. Inone aspect, the carbene precursors are selected from the groupconsisting of Compound 1-Compound 75.

Also provided are ruthenium carbene complexes selected from the groupconsisting of Compound 76-Compound 82.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an organic light emitting device.

FIG. 2 shows an inverted organic light emitting device that does nothave a separate electron transport layer.

FIG. 3 shows the general structure of the carbene precursors that can bereacted with osmium and ruthenium according to the provided method.

DETAILED DESCRIPTION

Generally, an OLED comprises at least one organic layer disposed betweenand electrically connected to an anode and a cathode. When a current isapplied, the anode injects holes and the cathode injects electrons intothe organic layer(s). The injected holes and electrons each migratetoward the oppositely charged electrode. When an electron and holelocalize on the same molecule, an “exciton,” which is a localizedelectron-hole pair having an excited energy state, is formed. Light isemitted when the exciton relaxes via a photoemissive mechanism. In somecases, the exciton may be localized on an excimer or an exciplex.Non-radiative mechanisms, such as thermal relaxation, may also occur,but are generally considered undesirable.

The initial OLEDs used emissive molecules that emitted light from theirsinglet states (“fluorescence”) as disclosed, for example, in U.S. Pat.No. 4,769,292, which is incorporated by reference in its entirety.Fluorescent emission generally occurs in a time frame of less than 10nanoseconds.

More recently, OLEDs having emissive materials that emit light fromtriplet states (“phosphorescence”) have been demonstrated. Baldo et al.,“Highly Efficient Phosphorescent Emission from OrganicElectroluminescent Devices,” Nature, vol. 395, 151-154, 1998;(“Baldo-I”) and Baldo et al., “Very high-efficiency green organiclight-emitting devices based on electrophosphorescence,” Appl. Phys.Lett., vol. 75, No. 3, 4-6 (1999) (“Baldo-II”), which are incorporatedby reference in their entireties. Phosphorescence is described in moredetail in U.S. Pat. No. 7,279,704 at cols. 5-6, which are incorporatedby reference.

FIG. 1 shows an organic light emitting device 100. The figures are notnecessarily drawn to scale. Device 100 may include a substrate 110, ananode 115, a hole injection layer 120, a hole transport layer 125, anelectron blocking layer 130, an emissive layer 135, a hole blockinglayer 140, an electron transport layer 145, an electron injection layer150, a protective layer 155, and a cathode 160. Cathode 160 is acompound cathode having a first conductive layer 162 and a secondconductive layer 164. Device 100 may be fabricated by depositing thelayers described, in order. The properties and functions of thesevarious layers, as well as example materials, are described in moredetail in U.S. Pat. No. 7,279,704 at cols. 6-10, which are incorporatedby reference.

More examples for each of these layers are available. For example, aflexible and transparent substrate-anode combination is disclosed inU.S. Pat. No. 5,844,363, which is incorporated by reference in itsentirety. An example of a p-doped hole transport layer is m-MIDATA dopedwith F.sub.4-TCNQ at a molar ratio of 50:1, as disclosed in U.S. PatentApplication Publication No. 2003/0230980, which is incorporated byreference in its entirety. Examples of emissive and host materials aredisclosed in U.S. Pat. No. 6,303,238 to Thompson et al., which isincorporated by reference in its entirety. An example of an n-dopedelectron transport layer is BPhen doped with Li at a molar ratio of 1:1,as disclosed in U.S. Patent Application Publication No. 2003/0230980,which is incorporated by reference in its entirety. U.S. Pat. Nos.5,703,436 and 5,707,745, which are incorporated by reference in theirentireties, disclose examples of cathodes including compound cathodeshaving a thin layer of metal such as Mg:Ag with an overlyingtransparent, electrically-conductive, sputter-deposited ITO layer. Thetheory and use of blocking layers is described in more detail in U.S.Pat. No. 6,097,147 and U.S. Patent Application Publication No.2003/0230980, which are incorporated by reference in their entireties.Examples of injection layers are provided in U.S. Patent ApplicationPublication No. 2004/0174116, which is incorporated by reference in itsentirety. A description of protective layers may be found in U.S. PatentApplication Publication No. 2004/0174116, which is incorporated byreference in its entirety.

FIG. 2 shows an inverted OLED 200. The device includes a substrate 210,a cathode 215, an emissive layer 220, a hole transport layer 225, and ananode 230. Device 200 may be fabricated by depositing the layersdescribed, in order. Because the most common OLED configuration has acathode disposed over the anode, and device 200 has cathode 215 disposedunder anode 230, device 200 may be referred to as an “inverted” OLED.Materials similar to those described with respect to device 100 may beused in the corresponding layers of device 200. FIG. 2 provides oneexample of how some layers may be omitted from the structure of device100.

The simple layered structure illustrated in FIGS. 1 and 2 is provided byway of non-limiting example, and it is understood that embodiments ofthe invention may be used in connection with a wide variety of otherstructures. The specific materials and structures described areexemplary in nature, and other materials and structures may be used.Functional OLEDs may be achieved by combining the various layersdescribed in different ways, or layers may be omitted entirely, based ondesign, performance, and cost factors. Other layers not specificallydescribed may also be included. Materials other than those specificallydescribed may be used. Although many of the examples provided hereindescribe various layers as comprising a single material, it isunderstood that combinations of materials, such as a mixture of host anddopant, or more generally a mixture, may be used. Also, the layers mayhave various sublayers. The names given to the various layers herein arenot intended to be strictly limiting. For example, in device 200, holetransport layer 225 transports holes and injects holes into emissivelayer 220, and may be described as a hole transport layer or a holeinjection layer. In one embodiment, an OLED may be described as havingan “organic layer” disposed between a cathode and an anode. This organiclayer may comprise a single layer, or may further comprise multiplelayers of different organic materials as described, for example, withrespect to FIGS. 1 and 2.

Structures and materials not specifically described may also be used,such as OLEDs comprised of polymeric materials (PLEDs) such as disclosedin U.S. Pat. No. 5,247,190 to Friend et al., which is incorporated byreference in its entirety. By way of further example, OLEDs having asingle organic layer may be used. OLEDs may be stacked, for example asdescribed in U.S. Pat. No. 5,707,745 to Forrest et al, which isincorporated by reference in its entirety. The OLED structure maydeviate from the simple layered structure illustrated in FIGS. 1 and 2.For example, the substrate may include an angled reflective surface toimprove out-coupling, such as a mesa structure as described in U.S. Pat.No. 6,091,195 to Forrest et al., and/or a pit structure as described inU.S. Pat. No. 5,834,893 to Bulovic et al., which are incorporated byreference in their entireties.

Unless otherwise specified, any of the layers of the various embodimentsmay be deposited by any suitable method. For the organic layers,preferred methods include thermal evaporation, ink-jet, such asdescribed in U.S. Pat. Nos. 6,013,982 and 6,087,196, which areincorporated by reference in their entireties, organic vapor phasedeposition (OVPD), such as described in U.S. Pat. No. 6,337,102 toForrest et al., which is incorporated by reference in its entirety, anddeposition by organic vapor jet printing (OVJP), such as described inU.S. patent application Ser. No. 10/233,470, which is incorporated byreference in its entirety. Other suitable deposition methods includespin coating and other solution based processes. Solution basedprocesses are preferably carried out in nitrogen or an inert atmosphere.For the other layers, preferred methods include thermal evaporation.Preferred patterning methods include deposition through a mask, coldwelding such as described in U.S. Pat. Nos. 6,294,398 and 6,468,819,which are incorporated by reference in their entireties, and patterningassociated with some of the deposition methods such as ink-jet and OVJD.Other methods may also be used. The materials to be deposited may bemodified to make them compatible with a particular deposition method.For example, substituents such as alkyl and aryl groups, branched orunbranched, and preferably containing at least 3 carbons, may be used insmall molecules to enhance their ability to undergo solution processing.Substituents having 20 carbons or more may be used, and 3-20 carbons isa preferred range. Materials with asymmetric structures may have bettersolution processibility than those having symmetric structures, becauseasymmetric materials may have a lower tendency to recrystallizeDendrimer substituents may be used to enhance the ability of smallmolecules to undergo solution processing.

Devices fabricated in accordance with embodiments of the invention maybe incorporated into a wide variety of consumer products, including flatpanel displays, computer monitors, televisions, billboards, lights forinterior or exterior illumination and/or signaling, heads up displays,fully transparent displays, flexible displays, laser printers,telephones, cell phones, personal digital assistants (PDAs), laptopcomputers, digital cameras, camcorders, viewfinders, micro-displays,vehicles, a large area wall, theater or stadium screen, or a sign.Various control mechanisms may be used to control devices fabricated inaccordance with the present invention, including passive matrix andactive matrix. Many of the devices are intended for use in a temperaturerange comfortable to humans, such as 18 degrees C. to 30 degrees C., andmore preferably at room temperature (20-25 degrees C.).

The materials and structures described herein may have applications indevices other than OLEDs. For example, other optoelectronic devices suchas organic solar cells and organic photodetectors may employ thematerials and structures. More generally, organic devices, such asorganic transistors, may employ the materials and structures.

The terms halo, halogen, alkyl, cycloalkyl, alkenyl, alkynyl, arylkyl,heterocyclic group, aryl, aromatic group, and heteroaryl are known tothe art, and are defined in U.S. Pat. No. 7,279,704 at cols. 31-32,which are incorporated herein by reference.

Bis-tridentate carbene complexes of osmium and ruthenium complexes haveunique properties in OLED applications, including extremely narrow linewidths and short excited state lifetimes. However, the synthesis ofthese types of compounds has been problematic due to the low yield inthe final step of complex formation, i.e. formation of the osmium orruthenium carbene complex. Therefore, because of the desirability ofthese compounds for OLED applications, and the need for higher yields, anew method was needed to prepare compounds of formula I.

In a previous patent publication, WO2009046266, incorporated herein byreference, only a low 2-5% yield was obtained for the synthesis of abis-tridentate osmium carbene complex. One of the challenges insynthesizing bis-tridentate carbene complexes of ruthenium and osmium ingood yield is believed to stem from the difficulty in simultaneouslyactivating the central aryl C—H bond along with the two N-heterocycliccarbene (NHC)C—H bonds in a single ligand. Since two deprotonations anda concurrent C—H activation are required, there have been limitedexamples of these complexes in the literature.

This difficulty has now been overcome by using a novel synthetic methodto obtain the corresponding bis-tridentate carbene complexes in goodyields. Table 1 illustrates various osmium metal salts used in thesynthesis of bis-tridentate-osmium carbene complexes and using compound35 and compound 75 as the carbene precursor. In one embodiment, theosmium or ruthenium halides in the +2 oxidation state are complexed withDMSO (dimethylsulfoxide), e.g. OsCl₂(DMSO)₄, RuCl₂(DMSO)₄.

Without being bound by theory, it is believed that the relative labilityof the DMSO ligands allows for their facile displacement, and thesubsequent complexation of the metal center with the carbene ligandsprovides the corresponding bis-tridentate osmium or ruthenium carbenecomplexes in good yield. For example, the reaction of OsCl₂(DMSO)₄ withsilver oxide, and compound 35 as carbene precursor in 2-ethoxyethanolprovided the corresponding osmium complex in 34% yield. An analogousreaction using RuCl₂(DMSO)₄ and compound 33 as the carbene precursorprovided the corresponding ruthenium complex in 46% yield. Thus, othersolvates of osmium(II) and ruthenium(II) halides are expected to beuseful. In one embodiment, THF (tetrahydrofuran) and CH₃CN solvates ofosmium(II) and ruthenium(II) halides can be used. In comparison toOsCl₂(DMSO)₄, the other osmium complexes resulted in significantly loweryields.

TABLE 1 Effect of Metal Precursor on Yield of Bis-tridentate CarbeneComplexes Using Compounds 35 and 75 as Carbene Precursor Method inDeprotonation Agent Ligation Experimental of NHC C—H bond Os PrecursorYield (%) Section Ag₂O OsCl₂(DMSO)₄ 34 A Ag₂O OsCl₂(PPh₃)₃ 4 B K₂CO₃OsH₆((i-Pr)₃)₂ 12 C Ag₂O [OsCl₂(benzene)]₂ 4 D Ag₂O Os₃(CO)₁₂ No productdetected

NHC derivatives that contain benzothiazole (i.e. N,S carbenes) andbenzoxazole (i.e. N,O carbenes) functionality tend to be less stablethan the corresponding imidazole or benzimidazole (i.e. N,N carbene)derivatives. Unlike N-substituted N,N carbenes, the carbene center inN,S and N,O carbenes is less sterically protected because the oxygen orsulfur atoms in these carbene derivatives cannot be substituted with,for example, an alkyl or aryl group. It was observed that synthesis ofN,S and N,O containing carbene precursors did not proceed using silveroxide, and another method had to be developed. It was surprisinglydiscovered that a combination of copper(I) chloride and an alkali metalalkoxide as the carbene forming agent, instead of silver(I) oxide,allowed for the synthesis of N,S and N,O containing carbene complexes ofosmium and ruthenium. Without being bound by theory, it is believed thata mixture of copper(I) chloride and an alkali metal alkoxide generates areactive copper(I) alkoxide species. In one embodiment, the carbeneforming agent is copper(I) alkoxide. In one embodiment the carbeneforming agent is copper(I) tert-butoxide. In one embodiment, the methodcomprises using copper(I) chloride an alkali metal tert-butoxide ascarbene forming agent, a N,S or N,O carbene precursor, and a suitableosmium or ruthenium metal salt to provide the N,S or N,O bis-tridentatecarbene complexes described herein. The use of copper(I) chloride analkali metal alkoxide is believed to be novel.

Accordingly, a method of making a metal complex having the formula I isprovided.Q₁-M-Q₂  Formula IThe method comprises mixing a salt of formula MX₂L_(n) with precursorsof carbenes Q₁ and Q₂, wherein Q₁ and Q₂ selected from a compound offormula II, which may be the same or different

a carbene forming agent, solvent, and heating the reaction mixture.Compounds of formula I are believed to be useful materials in OLEDapplications.

In the metal salt MX₂L_(n), M is a second or third row transition metalin the +2 oxidation state, X is a halogen, L is a ligand coordinated toM selected from the group consisting of DMSO, THF, and CH₃CN, and n is 2to 4. In one embodiment, M is ruthenium or osmium.

In one embodiment, the carbene forming agent is selected from silveroxide and copper(I) chloride. In one embodiment, the metal salt has theformula RuX₂(DMSO)₄. In one embodiment, the metal salt has the formulaRuCl₂(DMSO)₄. In one embodiment, the metal salt has the formulaOsX₂(DMSO)₄. In one embodiment, the metal salt has the formulaRuCl₂(DMSO)₄.

In one embodiment, the solvent comprises a polar solvent. In oneembodiment, the polar solvent comprises an alcohol. In one embodiment,the alcohol is selected from the group consisting of 2-methoxyethanol,2-ethoxyethanol, and mixtures thereof. Polar solvents such as alcoholsare desirable due to their capacity to effectively solvate polar speciessuch as carbene precursors Q₁ and Q₂.

Rings A and B are independently selected from the group consisting of:(a) a 5-membered heterocyclic group, (b) an 8- to 12-membered bicyclicgroup having from 0 to 6 ring heteroatoms, (c) an 11- to 18-memberedtricyclic group having from 0 to 7 ring heteroatoms, (d) an 11- to14-membered fused tricyclic group having from 0 to 6 ring heteroatoms,and (e) an 14- to 18-membered fused tetracyclic group having from 0 to 7ring heteroatoms. Ring A and/or ring B may form a salt, a is 0 to 4, andb is 0 to 4.

X¹ is selected from C—R¹ and N, X² is selected from C—R² and N, and X³is selected from C—R³ and N.

In one aspect, R¹ and R², or R² and R³ are linked to form a 5- or6-membered cyclic group, an 8- to 10-membered fused bicyclic group, an11- to 14-membered fused tricyclic group, which may be optionallysubstituted with one or more substituents independently selected fromhydrogen, deuterium, halide, alkyl, cycloalkyl, heteroalkyl, arylalkyl,alkoxy, aryloxy, amino, silyl, alkenyl, cycloalkenyl, heteroalkenyl,alkynyl, aryl, heteroaryl, acyl, carbonyl, carboxylic acids, ester,nitrile, isonitrile, sulfanyl, sulfinyl, sulfonyl, phosphino, andcombinations thereof;

In one aspect, R¹ and an R^(A) are linked to form a 5- or 6-memberedcyclic group, or an 8- to 10-membered fused bicyclic group.

In one aspect, R³ and an R^(B) are linked to form a 5- or 6-memberedcyclic group, or an 8- to 10-membered fused bicyclic group.

The groups R^(A), R^(B), R¹, R², R³, and R′ are independently selectedfrom the group consisting of hydrogen, deuterium, halide, alkyl,cycloalkyl, heteroalkyl, arylalkyl, alkoxy, aryloxy, amino, silyl,alkenyl, cycloalkenyl, heteroalkenyl, alkynyl, aryl, heteroaryl, acyl,carbonyl, carboxylic acids, ester, nitrile, isonitrile, sulfanyl,sulfinyl, sulfonyl, phosphino, and combinations thereof.

In one aspect, the precursors of carbenes Q₁ and Q₂ are independentlyselected from a compound of formula III:

In the compound of formula III, the dashed line represents an optionalbond, X⁴ is selected from N—R′, O, and S, X⁵ is selected from N—R′, O,and S, and A is a counterion.

Specific, non-limiting examples of carbene precursors are provided. Inone aspect, the carbene precursors are selected from the groupconsisting of Compound 1-Compound 74.

In one embodiment, the precursors of carbenes Q₁ and Q₂ areindependently selected from the group consisting of:

Also provided are ruthenium carbene complexes selected from the groupconsisting of:

Combination with Other Materials

The materials described herein as useful for a particular layer in anorganic light emitting device may be used in combination with a widevariety of other materials present in the device. For example, emissivedopants disclosed herein may be used in conjunction with a wide varietyof hosts, transport layers, blocking layers, injection layers,electrodes and other layers that may be present. The materials describedor referred to below are non-limiting examples of materials that may beuseful in combination with the compounds disclosed herein, and one ofskill in the art can readily consult the literature to identify othermaterials that may be useful in combination.

HIL/HTL:

A hole injecting/transporting material to be used in some embodiments ofthe present invention is not particularly limited, and any compound maybe used as long as the compound is typically used as a holeinjecting/transporting material. Examples of the material may include,but are not limited to: a phthalocyanine or porphryin derivative; anaromatic amine derivative; an indolocarbazole derivative; a polymercontaining fluorohydrocarbon; a polymer with conductivity dopants; aconducting polymer, such as PEDOT/PSS; a self-assembly monomer derivedfrom compounds such as phosphonic acid and sliane derivatives; a metaloxide derivative, such as MoO_(x); a p-type semiconducting organiccompound, such as 1,4,5,8,9,12-Hexaazatriphenylenehexacarbonitrile; ametal complex, and a cross-linkable compounds.

Examples of aromatic amine derivatives used in HIL or HTL may include,but are not limited to, the following general structures:

Each of Ar¹ to Ar⁹ is selected from the group consisting aromatichydrocarbon cyclic compounds such as benzene, biphenyl, triphenyl,triphenylene, naphthalene, anthracene, phenalene, phenanthrene,fluorene, pyrene, chrysene, perylene, azulene; group consisting aromaticheterocyclic compounds such as dibenzothiophene, dibenzofuran,dibenzoselenophene, furan, thiophene, benzofuran, benzothiophene,benzoselenophene, carbazole, indolocarbazole, pyridylindole,pyrrolodipyridine, pyrazole, imidazole, triazole, oxazole, thiazole,oxadiazole, oxatriazole, dioxazole, thiadiazole, pyridine, pyridazine,pyrimidine, pyrazine, triazine, oxazine, oxathiazine, oxadiazine,indole, benzimidazole, indazole, indoxazine, benzoxazole, benzisoxazole,benzothiazole, quinoline, isoquinoline, cinnoline, quinazoline,quinoxaline, naphthyridine, phthalazine, pteridine, xanthene, acridine,phenazine, phenothiazine, phenoxazine, benzofuropyridine,furodipyridine, benzothienopyridine, thienodipyridine,benzoselenophenopyridine, and selenophenodipyridine; and groupconsisting 2 to 10 cyclic structural units which are groups of the sametype or different types selected from the aromatic hydrocarbon cyclicgroup and the aromatic heterocyclic group and are bonded to each otherdirectly or via at least one of oxygen atom, nitrogen atom, sulfur atom,silicon atom, phosphorus atom, boron atom, chain structural unit and thealiphatic cyclic group. Each Ar is further substituted by a substituentselected from the group consisting of hydrogen, deuterium, halide,alkyl, cycloalkyl, heteroalkyl, arylalkyl, alkoxy, aryloxy, amino,silyl, alkenyl, cycloalkenyl, heteroalkenyl, alkynyl, aryl, heteroaryl,acyl, carbonyl, carboxylic acids, ester, nitrile, isonitrile, sulfanyl,sulfinyl, sulfonyl, phosphino, and combinations thereof.

In one aspect, Ar¹ to Ar⁹ is independently selected from the groupconsisting of:

k is an integer from 1 to 20; X¹ to X⁸ is CH or N; Ar¹ has the samegroup defined above.

Examples of metal complexes that may used in HIL or HTL include, but arenot limited to, the following general formula:

M is a metal having an atomic weight greater than 40; (Y¹-Y²) is abidentate ligand, Y¹ and Y² are independently selected from C, N, O, P,and S; L is an ancillary ligand; m is an integer value from 1 to themaximum number of ligands that may be attached to the metal; and m+n isthe maximum number of ligands that may be attached to the metal.

In one aspect, (Y¹-Y²) is a 2-phenylpyridine derivative.

In one aspect, (Y¹-Y²) is a carbene ligand.

In one aspect, M is selected from Ir, Pt, Os, and Zn.

In a further aspect, the metal complex has a smallest oxidationpotential in solution vs. Fc⁺/Fc couple less than about 0.6 V.

Host:

The light emitting layer of the organic EL device in some embodiments ofthe present invention preferably contains at least a metal complex aslight emitting material, and may contain a host material using the metalcomplex as a dopant material. Examples of the host material are notparticularly limited, and any metal complexes or organic compounds maybe used as long as the triplet energy of the host is larger than that ofthe dopant.

Examples of metal complexes used as host materials are preferred to havethe following general formula:

M is a metal; (Y³-Y⁴) is a bidentate ligand, Y³ and Y⁴ are independentlyselected from C, N, O, P, and S; L is an ancillary ligand; m is aninteger value from 1 to the maximum number of ligands that may beattached to the metal; and m+n is the maximum number of ligands that maybe attached to the metal.

In one aspect, the metal complexes are:

(O—N) is a bidentate ligand, having metal coordinated to atoms O and N.

In one aspect, M is selected from Ir and Pt.

In a further aspect, (Y³-Y⁴) is a carbene ligand.

Examples of organic compounds used as host materials include materialsselected from the group consisting of: aromatic hydrocarbon cycliccompounds such as benzene, biphenyl, triphenyl, triphenylene,naphthalene, anthracene, phenalene, phenanthrene, fluorene, pyrene,chrysene, perylene, azulene; group consisting aromatic heterocycliccompounds such as dibenzothiophene, dibenzofuran, dibenzoselenophene,furan, thiophene, benzofuran, benzothiophene, benzoselenophene,carbazole, indolocarbazole, pyridylindole, pyrrolodipyridine, pyrazole,imidazole, triazole, oxazole, thiazole, oxadiazole, oxatriazole,dioxazole, thiadiazole, pyridine, pyridazine, pyrimidine, pyrazine,triazine, oxazine, oxathiazine, oxadiazine, indole, benzimidazole,indazole, indoxazine, benzoxazole, benzisoxazole, benzothiazole,quinoline, isoquinoline, cinnoline, quinazoline, quinoxaline,naphthyridine, phthalazine, pteridine, xanthene, acridine, phenazine,phenothiazine, phenoxazine, benzofuropyridine, furodipyridine,benzothienopyridine, thienodipyridine, benzoselenophenopyridine, andselenophenodipyridine; and group consisting 2 to 10 cyclic structuralunits which are groups of the same type or different types selected fromthe aromatic hydrocarbon cyclic group and the aromatic heterocyclicgroup and are bonded to each other directly or via at least one ofoxygen atom, nitrogen atom, sulfur atom, silicon atom, phosphorus atom,boron atom, chain structural unit and the aliphatic cyclic group. Eachgroup is further substituted by a substituent selected from the groupconsisting of hydrogen, deuterium, halide, alkyl, cycloalkyl,heteroalkyl, arylalkyl, alkoxy, aryloxy, amino, silyl, alkenyl,cycloalkenyl, heteroalkenyl, alkynyl, aryl, heteroaryl, acyl, carbonyl,carboxylic acids, ester, nitrile, isonitrile, sulfanyl, sulfinyl,sulfonyl, phosphino, and combinations thereof.

In one aspect, the host compound contains at least one of the followinggroups in the molecule:

R¹ to R⁷ is independently selected from the group consisting ofhydrogen, deuterium, halide, alkyl, cycloalkyl, heteroalkyl, arylalkyl,alkoxy, aryloxy, amino, silyl, alkenyl, cycloalkenyl, heteroalkenyl,alkynyl, aryl, heteroaryl, acyl, carbonyl, carboxylic acids, ester,nitrile, isonitrile, sulfanyl, sulfinyl, sulfonyl, phosphino, andcombinations thereof, when it is aryl or heteroaryl, it has the similardefinition as Ar's mentioned above.

k is an integer from 0 to 20.

X¹ to X⁸ is selected from CH or N.

HBL:

A hole blocking layer (HBL) may be used to reduce the number of holesand/or excitons that leave the emissive layer. The presence of such ablocking layer in a device may result in substantially higherefficiencies as compared to a similar device lacking a blocking layer.Also, a blocking layer may be used to confine emission to a desiredregion of an OLED.

In one aspect, the compound used in the HBL contains the same moleculeused as host described above.

In one aspect, the compound used in the HBL contains at least one of thefollowing groups in the molecule:

k is an integer from 0 to 20; L is an ancillary ligand, m is an integerfrom 1 to 3.

ETL:

The electron transport layer (ETL) may include a material capable oftransporting electrons. The electron transport layer may be intrinsic(undoped) or doped. Doping may be used to enhance conductivity. Examplesof the ETL material are not particularly limited, and any metalcomplexes or organic compounds may be used as long as they are typicallyused to transport electrons.

In one aspect, the compound used in the ETL contains at least one of thefollowing groups in the molecule:

R¹ is selected from the group consisting of hydrogen, deuterium, halide,alkyl, cycloalkyl, heteroalkyl, arylalkyl, alkoxy, aryloxy, amino,silyl, alkenyl, cycloalkenyl, heteroalkenyl, alkynyl, aryl, heteroaryl,acyl, carbonyl, carboxylic acids, ester, nitrile, isonitrile, sulfanyl,sulfinyl, sulfonyl, phosphino, and combinations thereof, it has thesimilar definition as Ar's mentioned above.

Ar¹ to Ar³ has the similar definition as Ar's mentioned above.

k is an integer from 0 to 20.

X¹ to X⁸ is selected from CH or N.

In one aspect, the metal complexes used in the ETL may contain, but arenot limit to, the following general formula:

(O—N) or (N—N) is a bidentate ligand, having metal coordinated to atomsO, N or N,N; L is an ancillary ligand; m is an integer value from 1 tothe maximum number of ligands that may be attached to the metal.

In any above-mentioned compounds used in each layer of OLED device, thehydrogen atoms can be partially or fully deuterated.

In addition to and/or in combination with the materials disclosedherein, many hole injection materials, hole transporting materials, hostmaterials, dopant materials, exiton/hole blocking layer materials,electron transporting and electron injecting materials may be used in anOLED. Non-limiting examples of the materials that may be used in an OLEDin combination with materials disclosed herein are listed in Table 2below. Table 2 lists non-limiting classes of materials, non-limitingexamples of compounds for each class, and references that disclose thematerials.

TABLE 2 MATERIAL EXAMPLES OF MATERIAL PUBLICATIONS Hole injectionmaterials Phthalocyanine and porphryin compounds

Appl. Phys. Lett. 69, 2160 (1996) Starburst triarylamines

J. Lumin. 72-74, 985 (1997) CF_(x) Fluorohydrocarbon polymer

Appl. Phys. Lett. 78, 673 (2001) Conducting polymers (e.g., PEDOT:PSS,polyaniline, polypthiophene)

Synth. Met. 87, 171 (1997) WO2007002683 Phosphonic acid and sliane SAMs

US20030162053 Triarylamine or polythiophene polymers with conductivitydopants

EA01725079A1 and

Arylamines complexed with metal oxides such as molybdenum and tungstenoxides

SID Symposium Digest, 37, 923 (2006) WO2009018009 Semiconducting organiccomplexes

US20020158242 Metal organometallic complexes

US20060240279 Cross-linkable compounds

US20080220265 Hole transporting materials Triarylamines (e.g., TPD,α-NPD)

Appl. Phys. Lett. 51, 913 (1987)

U.S. Pat. No. 5,061,569

EP650955

J. Mater. Chem. 3, 319 (1993)

Appl. Phys. Lett. 90, 183503 (2007)

Appl. Phys. Lett. 90, 183503 (2007) Triaylamine on spirofluorene core

Synth. Met. 91, 209 (1997) Arylamine carbazole compounds

Adv. Mater. 6, 677 (1994), US20080124572 Triarylamine with(di)benzothiophene/ (di)benzofuran

US20070278938, US20080106190 Indolocarbazoles

Synth. Met. 111, 421 (2000) Isoindole compounds

Chem. Mater. 15, 3148 (2003) Metal carbene complexes

US20080018221 Phosphorescent OLED host materials Red hostsArylcarbazoles

Appl. Phys. Lett. 78, 1622 (2001) Metal 8-hydroxyquinolates (e.g., Alq₃,BAlq)

Nature 395, 151 (1998)

US20060202194

WO2005014551

WO2006072002 Metal phenoxybenzothiazole compounds

Appl. Phys. Lett. 90, 123509 (2007) Conjugated oligomers and polymers(e.g., polyfluorene)

Org. Electron. 1, 15 (2000) Aromatic fused rings

WO2009066779, WO2009066778, WO2009063833, US20090045731, US20090045730,WO2009008311, US20090008605, US20090009065 Zinc complexes

WO2009062578 Green hosts Arylcarbazoles

Appl. Phys. Lett. 78, 1622 (2001)

US20030175553

WO2001039234 Aryltriphenylene compounds

US20060280965

US20060280965

WO2009021126 Donor acceptor type molecules

WO2008056746 Aza-carbazole/DBT/DBF

JP2008074939 Polymers (e.g., PVK)

Appl. Phys. Lett. 77, 2280 (2000) Spirofluorene compounds

WO2004093207 Metal phenoxybenzooxazole compounds

WO2005089025

WO2006132173

JP200511610 Spirofluorene-carbazole compounds

JP2007254297

JP2007254297 Indolocabazoles

WO2007063796

WO2007063754 5-member ring electron deficient heterocycles (e.g.,triazole, oxadiazole)

J. Appl. Phys. 90, 5048 (2001)

WO2004107822 Tetraphenylene complexes

US20050112407 Metal phenoxypyridine compounds

WO2005030900 Metal coordination complexes (e.g., Zn, Al withN{circumflex over ( )}N ligands)

US20040137268, US20040137267 Blue hosts Arylcarbazoles

Appl. Phys. Lett, 82, 2422 (2003)

US20070190359 Dibenzothiophene/ Dibenzofuran- carbazole compounds

WO2006114966, US20090167162

US20090167162

WO2009086028

US20090030202, US20090017330 Silicon aryl compounds

US20050238919

WO2009003898 Silicon/Germanium aryl compounds

EP2034538A Aryl benzoyl ester

WO2006100298 High triplet metal organometallic complex

U.S. Pat. No. 7,154,114 Phosphorescent dopants Red dopants Heavy metalporphyrins (e.g., PtOEP)

Nature 395, 151 (1998) Iridium(III) organometallic complexes

Appl. Phys. Lett. 78, 1622 (2001)

US2006835469

US2006835469

US20060202194

US20060202194

US20070087321

US20070087321

Adv. Mater. 19, 739 (2007)

WO2009100991

WO2008101842 Platinum(II) organometallic complexes

WO2003040257 Osminum(III) complexes

Chem. Mater. 17, 3532 (2005) Ruthenium(II) complexes

Adv. Mater. 17, 1059 (2005) Rhenium (I), (II), and (III) complexes

US20050244673 Green dopants Iridium(III) organometallic complexes

Inorg. Chem. 40, 1704 (2001) and its derivatives

US20020034656

U.S. Pat. No. 7,332,232

US20090108737

US20090039776

U.S. Pat. No. 6,921,915

U.S. Pat. No. 6,687,266

Chem. Mater. 16, 2480 (2004)

US20070190359

US 20060008670 JP2007123392

Adv. Mater. 16, 2003 (2004)

Angew. Chem. Int. Ed. 2006, 45, 7800

WO2009050290

US20090165846

US20080015355 Monomer for polymeric metal organometallic compounds

U.S. Pat. No. 7,250,226, U.S. Pat. No. 7,396,598 Pt(II) organometalliccomplexes, including polydentated ligands

Appl. Phys. Lett. 86, 153505 (2005)

Appl. Phys. Lett. 86, 153505 (2005)

Chem. Lett. 34, 592 (2005)

WO2002015645

US20060263635 Cu complexes

WO2009000673 Gold complexes

Chem. Commun. 2906 (2005) Rhenium(III) complexes

Inorg. Chem. 42, 1248 (2003) Deuterated organometallic complexes

US20030138657 Organometallic complexes with two or more metal centers

US20030152802

U.S. Pat. No. 7,090,928 Blue dopants Iridium(III) organometalliccomplexes

WO2002002714

WO2006009024

US20060251923

U.S. Pat. No. 7,393,599, WO2006056418, US20050260441, WO2005019373

U.S. Pat. No. 7,534,505

U.S. Pat. No. 7,445,855

US20070190359, US20080297033

U.S. Pat. No. 7,338,722

US20020134984

Angew. Chem. Int. Ed. 47, 1 (2008)

Chem. Mater. 18, 5119 (2006)

Inorg. Chem. 46, 4308 (2007)

WO2005123873

WO2005123873

WO2007004380

WO2006082742 Osmium(II) complexes

U.S. Pat. No. 7,279,704

Organometallics 23, 3745 (2004) Gold complexes

Appl. Phys. Lett. 74, 1361 (1999) Platinum(II) complexes

WO2006098120, WO2006103874 Exciton/hole blocking layer materialsBathocuprine compounds (e.g., BCP, BPhen)

Appl. Phys. Lett. 75, 4 (1999)

Appl. Phys. Lett. 79, 449 (2001) Metal 8-hydroxyquinolates (e.g., BAlq)

Appl. Phys. Lett. 81, 162 (2002) 5-member ring electron deficientheterocycles such as triazole, oxadiazole, imidazole, benzoimidazole

Appl. Phys. Lett. 81, 162 (2002) Triphenylene compounds

US20050025993 Fluorinated aromatic compounds

Appl. Phys. Lett. 79, 156 (2001) Phenothiazine-S-oxide

WO2008132085 Electron transporting materials Anthracene- benzoimidazolecompounds

WO2003060956

US20090179554 Aza triphenylene derivatives

US20090115316 Anthracene-benzothiazole compounds

Appl. Phys. Lett. 89, 063504 (2006) Metal 8-hydroxyquinolates (e.g.,Alq₃, Zrq₄)

Appl. Phys. Lett. 51, 913 (1987) U.S. Pat. No. 7,230,107 Metalhydroxybenoquinolates

Chem. Lett. 5, 905 (1993) Bathocuprine compounds such as BCP, BPhen, etc

Appl. Phys. Lett. 91, 263503 (2007)

Appl. Phys. Lett. 79, 449 (2001) 5-member ring electron deficientheterocycles (e.g., triazole, oxadiazole, imidazole, benzoimidazole)

Appl. Phys. Lett. 74, 865 (1999)

Appl. Phys. Lett. 55, 1489 (1989)

Jpn. J. Apply. Phys. 32, L917 (1993) Silole compounds

Org. Electron. 4, 113 (2003) Arylborane compounds

J. Am. Chem. Soc. 120, 9714 (1998) Fluorinated aromatic compounds

J. Am. Chem. Soc. 122, 1832 (2000) Fullerene (e.g., C60)

US20090101870 Triazine complexes

US20040036077 Zn (N{circumflex over ( )}N) complexes

U.S. Pat. No. 6,528,187

EXPERIMENTAL

Chemical abbreviations used throughout this document are as follows: DMFis dimethylformamide, Et₃N is triethylamine, PPh₃ istripheynylphosphine, P(i-Pr)₃ is triisopropylphosphine, EtOAc is ethylacetate, THF is tetrahydrofuran, DMSO is dimethylsulfoxide, DCM isdichloromethane.

Example 1 Synthesis of Ruthenium Complex of Compound 33 Synthesis of1,3-bis(1H-benzo[d]imidazol-1-yl)benzene

In a 1 L round-bottomed flask 1,3-diiodobenzene (26.43 g, 80 mmol),1H-benzo[d]imidazole (20.82 g, 176 mmol), and 1,10-phenanthroline (5.77g, 32.0 mmol), CuI (3.05 g, 16 mmol), and cesium carbonate (120 g, 369mmol) were combined in anhydrous DMF (350 mL) to give a brownsuspension. The reaction was purged with N₂ for 20 minutes and thenheated to reflux for 24 hours. The reaction mixture was passed thought aplug of silica gel (5% MeOH in DCM) to obtain the crude product. Thecrude product was subjected to silica gel chromatography (SiO₂, 400 g,2% MeOH to 5% MeOH in DCM) to ultimately obtain the final product (12.66g, 51%).

Synthesis of3,3′-(1,3-phenylene)bis(1-iodo-1-methyl-2,3-dihydro-1H-benzo[d]imidazol-1-ium-2-ide)[Compound 33]

In a 1 L round bottom flask, 1,3-bis(1H-benzo[d]imidazol-1-yl)benzene(12.66 g, 40.8 mmol), iodomethane (25.5 mL, 408 mmol) were combined inDMF (500 mL) to give a yellow solution. The reaction mixture was heatedto 42° C. for 24 hours and filtered to get the product (21.69 g, 89%).

Synthesis of Ruthenium Complex of Compound 33

A 1 L round-bottomed flask was charged with RuCl₂(DMSO)₄ (2 g, 4.13mmol), carbene ligand precursor compound 33 (7.36 g, 12.38 mmol),silver(I) oxide (5.74 g, 24.77 mmol) and 2-ethoxyethanol (400 mL) togive a tan suspension. The reaction mixture was vacuum evacuated,backfilled with N₂ and heated to reflux for 1 hour. The reaction mixturewas filtered and the filtrate was evaporated to dryness. The residueobtained after evaporation was subjected to column chromatography (SiO₂,pretreated with Et₃N, 50% DCM in hexanes) to yield the ruthenium complexof compound 1 (1070 mg, 33%).

Synthesis of 1,3-bis(3H-imidazo[4,5-b]pyridin-3-yl)benzene

A 500 mL round-bottomed flask was charged with1H-imidazo[4,5,-b]pyridine (12.7 g, 107 mmol), 1,3-diiodobenzene (17.65g, 53.5 mmol), copper (I) oxide (0.176 g, 1.231 mmol),4,7-dimethoxy-1,10-phenanthroline (0.591 g, 2.46 mmol), cesium carbonate(48.8 g, 150 mmol), polyethylene glycol (9.79 g, D=1.088, 9 mL) and DMSO(125 mL) The reaction mixture was vacuum evacuated and back filled withN₂ three times. The reaction mixture was heated to 110° C. for 24 hours.The reaction mixture was decanted into water (500 mL) and filtered. Theprecipitate was collected subjected to column chromatography (SiO₂, 5%MeOH in DCM) to yield the desired product (6 g, 36%).

Synthesis of Ruthenium Complex of Compound 53

A 1 L round-bottomed flask was charged with carbene precursor compound53 (2.98 g, 4.99 mmol), Ag₂O (2.31 g, 9.99 mmol) and 2-ethoxyethanol(390 mL) The reaction mixture was vacuum evacuated and back filled withN₂ three times. The reaction mixture was heated to 40° C. for 1 hour.The Ru precursor (1.1 g, 2.27 mmol) was then added and the reactionmixture was refluxed for 1 hour. The reaction mixture was filtered andthe filtrate was evaporated to dryness. The residue obtained afterevaporation was subjected to column (SiO₂, pretreated with Et₃N, 70% DCMin hexanes) to yield the title complex (0.82 g, 46%).

Synthesis of OsCl₂(DMSO)₄

An aqueous solution of [NH₄]₂[OsCl₆] (1 g, 2.278 mmol) was passedthrough a cation exchange column in the protic form, eluted with water,after which the solvent was removed from the eluate using a rotatoryevaporator. The residue was transferred to a Schlenk tube as a solutionin methanol and the solvent removed in vacuo. The resulting red-blackresidue was dissolved in DMSO (5 mL), and 5 nCl₂.2H₂O (0.8 g, 3.55 mmol)was added and the mixture was stirred under N₂ for 1 hour at 150° C. TheDMSO was removed by vacuum distillation. 20 mL of DCM was added into theresidue and the suspension was filtered through celite. The filtrate wasconcentrated and washed with acetone to yield the desired compound (0.7g, 53.6%)

Synthesis of OsCl₂(PPh₃)₃

(NH₄)₂OSCl₆+PPh₃→Oscl₂(PPh₃)₃

(NH₄)₂OsCl₆ (2.57 g, 5.85 mmol) and PPh₃ (10.82 g, 41.2 mmol) wererefluxed under nitrogen for 20 hours in a solvent mixture composed of385 mL tert-butyl alcohol and 154 mL water. After cooling to roomtemperature, the pale green solid was filtered, washed with water,methanol, and hexanes. The solid was dried under vacuum to yield thedesired product (5.65 g, 92%).

Synthesis of OsH₆(P(i-Pr)₃)₂

Step 1OsCl₃+P(i-Pr)₃→OsH₂Cl₂(P(i-Pr)₃)₂

A suspension of OsCl₃ (3.79 g, 12.77 mmol) in 40 mL of 2-propanol wastreated with P(i-Pr)₃ (12 g, 90% purity, 67.4 mmol) and heated for 24hours under reflux. After the mixture was cooled to room temperature, abrown-yellow precipitate was formed, which was filtered off, andrepeatedly washed with methanol and ether, and dried in vacuo to yieldOsH₂Cl₂(P(i-Pr)₃)₂ (2.11 g, 28.3%)

Step 2

A solution of OsH₂Cl₂(P(i-Pr)₃)₂ in 180 mL of toluene was first treatedwith NaBH₄ (1.737 g, 45.9 mmol) and then dropwise with 5 mL of methanol.After the reaction mixture was stirred for 30 minutes at roomtemperature, the solution was filtered. The filtrate was concentrated toca 0.5 mL in vacuo, and 10 mL of methanol was added. The solution wasagain concentrated until a white precipitate separated and then storedat −78° C. for 2 hours. The white precipitate was filtered off, washedwith small amount of methanol, and dried in vacuo: yield 0.37 g (15.6%).

Synthesis of [OsCl₂(benzene)]₂

A suspension of OsCl₃ (7.85 g, 26.5 mmol) in 100 mL of ethanol wastreated with cyclohexa-1,3-diene (2.12 g, 26.5 mmol) and heated for 48hours under reflux. The yellow precipitate was filtered off, washed witha small amount of methanol, and dried in vacuo: yield 7.26 g (81%).

Methods for Osmium Ligation Using Compound 35

Method A

A 250 mL round-bottomed flask was charged with OsCl₂(DMSO)₄ (250 mg,0.436 mmol), tridentate carbene precursor compound 35 (721 mg, 1.089mmol), and silver (I) oxide (505 mg, 2.179 mmol) in 2-ethoxyethanol (125mL) to give a tan suspension. The reaction mixture was vacuum evacuated,back filled with N₂ and heated to reflux for 1 hour. The reactionmixture was filtered thought celite and the filtrate was subject tocolumn chromatography (SiO₂, pretreated with Et₃N, 60% EtOAc in hexanes)to yield the desired compound (152 mg, 34%).

Method B

A 250 mL round-bottomed flask was charged with OsCl₂(PPh₃)₄ (250 mg,0.436 mmol), tridentate carbene precursor compound 35 (721 mg, 1.089mmol), and silver (I) oxide (505 mg, 2.179 mmol) in DMF (125 mL) to givea tan suspension. The reaction mixture was vacuum evacuated, back filledwith N₂, and heated to reflux for 1 hour. The reaction mixture wasfiltered thought celite and the filtrate was subject to columnchromatography (SiO₂, pretreated with Et₃N, 60% EtOAc in hexanes) toyield the desired compound (17 mg, 4%).

Method C

A 250 mL round-bottomed flask was charged with OsH₆((i-Pr)₃P)₂ (150 mg,0.29 mmol), tridentate carbene precursor compound 35 (404 mg, 0.61 mmol)and K₂CO₃ (401 mg, 2.9 mmol) in dioxane (100 mL) to give a tansuspension. The reaction mixture was vacuum evacuated, back filled withN₂ and heated to reflux for 7 hours. The reaction mixture was filteredthought celite and the filtrate was subject to column chromatography(SiO₂, pretreated with Et₃N, 30% DCM in hexanes) to yield desiredcompound (51 mg, 12%).

Method D

A 1 L round-bottomed flask was charged with silver (I) oxide (9.9 9 g,43.1 mmol), tridentate carbene precursor compound 75 (11.84 g, 21.56mmol) and DMF (700 mL). The reaction mixture was vacuum evacuated andback filled with N₂. It was stirred for 1 hour at room temperature. Thereaction mixture was filtered thought celite and the filtrate wastreated with [OsCl₂(benzene)]₂ (3.66 g, 5.39 mmol). The reaction mixturewas heated to 120° C. for 2 hours. The DMF was then removed by vacuumdistillation, and the residue was subjected to column chromatography(SiO₂, pretreated with Et₃N, EtOAc) to yield desired compound (334 mg,4%).

It is understood that the various embodiments described herein are byway of example only, and are not intended to limit the scope of theinvention. For example, many of the materials and structures describedherein may be substituted with other materials and structures withoutdeviating from the spirit of the invention. The present invention asclaimed may therefore includes variations from the particular examplesand preferred embodiments described herein, as will be apparent to oneof skill in the art. It is understood that various theories as to whythe invention works are not intended to be limiting.

The invention claimed is:
 1. A compound selected from the groupconsisting of:


2. The compound of claim 1, wherein said compound is


3. The compound of claim 1, wherein said compound is


4. The compound of claim 1, wherein said compound is


5. The compound of claim 1, wherein said compound is


6. The compound of claim 1, wherein said compound is


7. The compound of claim 1, wherein said compound is


8. The compound of claim 1, wherein said compound is


9. An organic light emitting device, comprising: an anode; a cathode;and an emissive layer, wherein the emissive layer comprises a compoundselected from the group consisting of:


10. The organic light emitting device of claim 9, wherein said compoundis


11. The organic light emitting device of claim 9, wherein said compoundis


12. The organic light emitting device of claim 9, wherein said compoundis


13. The organic light emitting device of claim 9, wherein said compoundis


14. The organic light emitting device of claim 9, wherein said compoundis


15. The organic light emitting device of claim 9, wherein said compoundis


16. The organic light emitting device of claim 9, wherein said compoundis


17. A formulation comprising a compound selected from the groupconsisting of: